diff --git a/tests/libtest/lib500.c b/tests/libtest/lib500.c
index bca5c2310e..8ebeb1292f 100644
--- a/tests/libtest/lib500.c
+++ b/tests/libtest/lib500.c
@@ -25,7 +25,7 @@
 
 #ifdef LIB585
 
-int counter;
+static int counter;
 
 static curl_socket_t tst_opensocket(void *clientp,
                                     curlsocktype purpose,